1. Field of the Invention
The present invention relates to an ion exchanger useful for separation and purification of a biogenic polymer such as a protein or a nucleic acid, and particularly to a packing material for liquid chromatography.
2. Discussion of Background
Heretofore, for purification of a biogenic polymer, particularly a protein, ion exchange chromatography has been often used as a purification method whereby the property change of the sample is little. As an ion exchanger which has been used for this purpose, a polysaccharide-type exchanger represented by an ion exchanger of a cellulose base material may be mentioned. However, when packed into a column, such an ion exchanger presents poor permeability, and its resolution is rather low, since the carrier particles cannot be made small enough. Also, the durability of the packed column was poor. Further, an ion exchanger of a crosslinked agarose base material or a crosslinked synthetic polymer base material has been developed as a commercial product. However, such a packing material has the drawback that as its hardness increases, the capacity for binding a sample such as a protein tends to decrease. To solve this problem, it has been proposed to prepare an ion exchanger by using a semi-rigid or chemically modified silica gel having hydroxyl groups as the base material, and to graft-polymerize an acrylamide derivative, an acrylic acid ester or vinyl acetate in the presence of a cerium (VI) salt as a catalyst to form a spacer, and it has been suggested that the capacity for binding a sample can thereby be improved (EP 337144A). However, the ion exchanger disclosed in this publication, wherein an oligomer of an acrylamide derivative or a (meth)acrylic acid ester is used as a spacer or a chemical bond-type silica gel is used as a base material, is gradually hydrolyzed when contacted with a strong acid or a strong base, whereby a decrease in the ion exchange capacity or in the capacity for binding a protein is observed. Washing of a separation column by means of a strong acid or a strong base is frequently used for cleaning the column, especially for the separation and purification of a biogenic polymer. Further, vinyl acetate is hardly graft-polymerized, and the resulting hydroxyl groups are all secondary hydroxyl groups and have poor reactivity, whereby it has been difficult to introduce ion exchange groups.
Among the above-mentioned various ion exchangers, there is no ion exchanger which is excellent in column permeability and which has a large capacity for binding a protein and excellent chemical stability against a reagent to be used for cleaning the column or for regeneration treatment.